pdfGetNumDeviceNChannels

Get number of color channels in DeviceN image.

int pdfGetNumDeviceNChannels(PDFHandle pdf)

This function returns the number of color channels generated by the
last call to pdfConvertPageToDeviceNImage. There will always be
at least four channels (for the process colors, cyan, magenta, yellow,
and black). There will be additional channels for any custom (spot)
colors used on the page.